The present invention relates to a method for controlling charging of an energy storage system in a vehicle comprising an electric machine which is arranged for propulsion of said vehicle, said method comprising: initiating said charging upon connection of said energy storage system to an external power supply via connector elements; and transmitting, between said vehicle and said external power supply, a control signal comprising data related to said charging by means of a wireless transmission link.
The present invention also relates to an arrangement for controlling charging of an energy storage system in a vehicle comprising an electric machine which is arranged for propulsion of said vehicle, said arrangement comprising an external power supply arranged for initiating charging upon connection of said energy storage system to the external power supply via connector elements, and a transmitter unit and receiver unit arranged for wirelessly transmitting a control signal comprising data related to said charging between said vehicle and said external power supply.
In the field of vehicles, there is a steady increase in research and development related to propulsion of vehicles with alternative power sources, i.e. power sources being used as alternatives to conventional internal combustion engines.
An internal combustion engine, for example in the form of a gasoline engine or a diesel engine, offers high efficiency with relatively low fuel consumption. However, environmental concerns have led to an increase in development of more environmental-friendly power sources for vehicles. In particular, the development of electrically operated vehicles has emerged as a promising alternative.
Today, there exist various types of vehicle propulsion systems comprising electric machines. For example, a vehicle can be operated by means of an electric machine solely, or by means of an arrangement comprising both an electric machine and an internal combustion engine. The latter alternative is often referred to as a hybrid vehicle (HEV), and can for example be utilized in a manner in which an internal combustion engine is used for operating the vehicle while driving outside urban areas whereas the electric machine can be used in urban areas or in environments in which there is a need to limit the discharge of harmful pollutants such as carbon monoxide and oxides of nitrogen.
The technology involved in electrically operated vehicles is closely related to the development of electrical energy storage systems, for example in the form of battery-related technology for vehicles. Today's electrical energy storage systems for vehicles may comprise a set of rechargeable battery cells which, together with control circuits, forms a unit which is arranged in a vehicle and which is configured for operating an electric machine. A hybrid vehicle is also often arranged so that the energy storage system is charged during braking, by means of a process known as regenerative braking.
A vehicle being operated by means of an internal combustion engine and an electric machine supplied with power from a rechargeable electrical energy storage system is sometimes referred to as a plug-in hybrid electric vehicle (PHEV). A plug-in hybrid electric vehicle uses an energy storage system with rechargeable batteries or another suitable energy source which can be restored into a condition involving a full charge through a connection to an external electric power supply.
The external power supply can be in the form of the common electric grid power system which can be accessed via a conventional power cord, or can be in the form of other arrangements depending on the vehicles involved and the power need for the recharging process. In case of vehicles in the form of buses or heavy transport vehicles, more powerful charging devices and procedures are normally needed as compared with smaller cars and similar vehicles.
A challenge for today's electrically driven vehicles, in particular heavy vehicles such as buses and trucks, is that a high amount of energy must be charged into the energy storage system in a relatively short time in order to optimize the vehicle's range of driving. For this reason, the actual charging of the energy storage system is suitably implemented through a process in which a control unit on the vehicle requests a charging to be carried out by means of an external electric power supply. This is carried out after the energy storage system and the external power supply have been electrically connected by means of suitable connector elements. In such cases, a so-called pantograph can for example be used to connect the onboard energy storage system with an external power supply.
The recharging of an energy storage system in a bus, for example, may involve charging an electrical energy storage system comprising a number of battery cells with a charging current which is of the magnitude 200 A, whereas the electrical energy storage system may have a voltage of the magnitude of 600 V. Such a charging procedure involves certain safety risks, for example if the battery cells are exposed to excessive heat, impact or overcharging, or if electrically conducting parts of the energy storage system or charging system come into contact with persons. A particular situation in which there may arise a safety risk is if the vehicle should move out of its position during the charging procedure. Consequently, there are demands for protection of persons and material in the event of any error which may occur during charging.
Also, the battery cells of the energy storage system are both very expensive and also very sensitive to overcharging. This also means that overcharging of the energy storage system must not occur.
Consequently, there is a demand for methods and arrangements by means of which the charging of an energy storage system in a hybrid vehicle can be carried out in a secure manner, in particular in the event that unexpected changes in certain parameters and conditions (such as the position of the vehicle, the temperature of the energy storage system etc.) should arise. In such situations, it is important that the charging procedure does not lead to any safety risks.
The patent document US 2011/078092 discloses a method and apparatus for controlling a battery. The apparatus is arranged for establishing a wireless communication link in order to transmit data related to battery charge management. The apparatus also comprises a controller arranged for generating a control signal comprising information related to a target capacity of an electric vehicle battery.
Even though the above-mentioned solution according to US 2011/078092 offers a reliable solution for controlling the charging procedure in a vehicle with electric propulsion, there are still further demands for a sufficiently high level of safety for persons and for electric equipment during charging of an energy storage system, in particular in hybrid vehicles.
It is desirable to provide an improved method and arrangement by means of which the above-mentioned problems can be overcome and, in particular, by means of which a charging procedure can be monitored and controlled in the event that any unexpected errors should occur.
In accordance with an aspect of the invention, a method is provided for controlling charging of an energy storage system in a vehicle comprising an electric machine which is arranged for propulsion of said vehicle, said method comprising: initiating said charging upon connection of said energy storage system to an external power supply via connector elements; and transmitting, between said vehicle and said external power supply, a control signal comprising data related to said charging by means of a wireless transmission link. The method furthermore comprises:
evaluating whether said control signal is received; and terminating said charging in the event that said control signal is not received.
By means of a method as defined above, there is provided a method for charging an energy storage system in which a very high degree of safety is obtained. In particular, the fact that the invention comprises an evaluation whether the control signal is received or not allows the charging to be discontinued in a number of situations which can be perceived as being a risk as regards personal safety or damage to goods and objects.
Preferably, the control signal is transmitted from said vehicle to said external power supply, wherein said evaluating is carried out in the external power supply.
Furthermore, the control signal can be in the form of a modulated radio signal which is transmitted by means of a radio transmitter unit in the vehicle; wherein the control signal is received by means of a radio receiver unit in the external power supply. The radio signal can be transmitted and received by means of a wireless short-range radio network.
The control signal is provided in different forms, suitably in at least one of the following forms:
i) a generally continuous signal having a predetermined frequency and/or amplitude;
ii) a generally pulse-shaped signal with a predetermined pulse width and/or amplitude; and
iii) a repeated sequence comprising a signal as defined in i) or ii) and a pause of predetermined length.
Consequently, the control signal can be designed in a number of ways depending on the type of equipment used as a receiving unit, in order to carry out the detection of the control signal in a simple and efficient manner.
Also, the control signal is configured so as to contain certain data related to the charging of the energy storage system, in particular so that the control signal can be used to terminate the charging depending on the current values of at least one of the following parameters:
i) the current position of said vehicle;
ii) any occurring movement of said vehicle;
iii) the identity of said vehicle;
iv) the electrical isolation of said electrical storage system;
v) the status of contact elements of high voltage components of said vehicle;
vi) the charging current;
vii) the charging voltage; and
viii) the temperature of said connector elements.
By using input in the form of at least one of the above-mentioned parameters, the transmission of the control signal can be used to terminate the charging process in the event that said at least one parameter deviates from a predetermined value.
Furthermore, according to an embodiment, the invention can be arranged to generate an alarm signal in the event that said charging is terminated due to the control signal not being received.
According to a particular embodiment, the invention can be arranged for providing a predetermined modulation of said control signal; and evaluating whether the charging supplied to said energy storage system comprises said predetermined modulation; and, if this is not the case, indicating that said charging of the energy storage system is erroneous. Suitably, the invention may comprise disconnecting the energy storage system from the external power supply in the event that said charging is terminated.
The above-mentioned problem is also solved by means of an arrangement for controlling charging of an energy storage system in a vehicle comprising an electric machine which is arranged for propulsion of said vehicle, said arrangement comprising an external power supply arranged for initiating charging upon connection of said energy storage system to the external power supply via connector elements, and a transmitter unit and receiver unit arranged for wirelessly transmitting a control signal comprising data related to said charging between said vehicle and said external power supply. The arrangement is configured for evaluating whether said control signal is received in said receiver unit and for terminating said charging in the event that said control signal is not received.
An advantage with the invention is that it provides a fast and reliable transfer of information related to commands for shutting down the charging of the energy storage system. This is provided by transmission, in a wireless manner, of a control signal in the form of a radio communication carrier wave.
If the carrier wave is not received in a proper manner, due to a high voltage-related error having been discovered in the vehicle, or due to any occurring interference or disturbance on the communication link, this should be interpreted as a command to terminate the charging of the energy storage system.
The invention can be implemented in a manner in which the control signal is transmitted from the vehicle to the external power supply or, inversely, from the external power supply to the vehicle.
The term “charging pattern” as used below refers to a predetermined schedule, sequence or progression of the recharging process of the energy storage system. Such a charging pattern can for example be in the form of a “quick charge”, i.e. involving a relatively high charging current during a relatively short time period, or a “standard charge”, i.e. involving a lower charging current during a relatively long time period. A charging pattern of the “quick charge” type can for example be suitable for recharging the energy storage system of a bus while the bus is being parked briefly during a lunch break or between two consecutive rounds. Consequently, a “charging pattern” is a charging sequence with a certain charging current and voltage which occurs for a certain time or until a certain state of charge has be achieved by the energy storage system
Furthermore, the term “modulation” refers to any predetermined variation, deviation or adaptation of the charging current or charging voltage which can be controlled by the vehicles control unit and requested to be supplied from the external power supply. According to a particular embodiment which is described below, such a “modulated” charging pattern can subsequently be detected and evaluated by the vehicles control unit in order to determine whether the charging supplied by the external power supply corresponds to the requested charging. Any difference between the requested charging pattern and the supplied charging pattern can be interpreted as an error of the charging process.